The impedance curve between the Fs peak and the VC inductance rise in the HF presents a pretty constant load, and this is the range that contains the 'heart' of most of the music. A 2-way speaker places a broad peak in the midst of that. Its very much like running a 16 ohm speaker on a 4 ohm tap. The sound just lacks vitality. IME, full range/wide range drivers present an easy load for tube amplifiers. At only 90 db/w/m, the RS 1354 is easily driven by my 45 SET, sounding a little more lively than 2-way Tannoys with a 1.5 kHz xover and 94 db/w/m. The impedance mismatch caused by a midrange crossover peak results in poor power transfer, less apparent (actual in the range of the peak) efficiency, and a less lively presentation.

Best,

Bob